The hypothalamic decapeptide gonadotropin-hormone-releasing hormone (GnRH), also known as lutenizing hormone-releasing-hormone (LHRH), functions as a key hormone in the regulation of mammalian reproduction. It is released from the hypothalamus and stimulates the synthesis and release of lutenizing hormone (LH) and follicle stimulating hormone (FSH). In addition to its classic hypophysiotropic action, GnRH functions as a modulator of the activity of diverse systems in the brain and many peripheral organs. It has been suggested that an autocrine/paracrine function of GnRH exists for example in the placenta, granulosa cells, myometrium and lymphoid cells. In addition, this GnRH based autocrine system seems to be present in a number of human malignant tumors including cancers of the ovary, endometrium, breast and other reproductive organs.
About 80% of the endometrial and ovarian cancers and about 50% of all breast cancers, and a large number of the malignant melanoma have GnRH receptors as part of their negative autocrine regulation system for cell proliferation. These types of cancer cells or tumor cells can also be identified as steroid-related or steroid-sensitive tumor cells. In normal tissue GnRH receptors are not present or only expressed very weakly.
The GnRH is a peptide and, today, various forms of the GnRH have been described. One type of GnRH is the mammalian GnRH (mGnRH or GnRH 1), which was first found in the mammalian hypothalamus. The second type of GnRH (GnRH 11) was described for the first time in chicken brain. GnRH II can be found in almost all vertebrates including mammalia. Beside the expression in the central nervous system the expression of GnRH-I and GnRH-II has been reported in tissues regulating the immune and reproductive system.
As mentioned above, it is known that the GnRH-I and its receptor represents a part of the negative autocrine regulation system for cell proliferation, of the cell cycle as well as in the anti-apoptosis system. The signalling pathway involved in the autocrine regulation system was studied in detail and it was demonstrated that GnRH-I via the nucleus factor kappa B (NF-κB) protects tumor cells from going into the apoptosis.
It was known that in tumor cells GnRH-I agonist and antagonist act in the same way, i.e. both display an anti-proliferative activity. That means, GnRH-I antagonists act like agonists indicating that the dichotomy of GnRH-I agonist and antagonist does not exist in tumor cells. Further, it is described that the anti-proliferative effect of the GnRH-I agonist can be abrogated in cells wherein the signalling pathway via the GnRH I receptor is interrupted. In contrast, the GnRH-I antagonist still has an anti-proliferative effect on this type of cells.
The exact amino acid sequence of the human GnRH-II receptor is not known, although various attempts have been made to clone the receptor and to obtain the complete nucleic acid sequence. Further, no successful characterization of the human GnRH-II receptor is given in the literature. The information known today about the GnRH-II receptor are based on data obtained from other mammalian species. For the human receptor, no functional transcript is described.
Agonists and antagonists of the GnRH type II molecules of non human mammalian species are described in the art. For example, WO 00/32218 describes pharmaceutical formulations containing GnRH II and antagonists thereof. In WO 03/093304 various agonists and antagonists of the GnRH II are disclosed useful for the treatment of reproductive physiology diseases and steroid-related cancer cells. It was demonstrated that the anti-proliferative effects of GnRH type II agonists as well as of the native GnRH II is higher than the anti-proliferative effect demonstrated for the GnRH I analoga.
It was known that GnRH I and GnRH II as well as GnRH I analoga and GnRH II agonists are able to influence the proliferation of tumor cells. That is, these molecules can decrease the proliferation rate of the tumor cells, thereby stopping or reducing the growth of the tumor. However, the ultimate goal in tumor treatment, the full disappearance of the tumor, i.e. the full remission of the tumor, can not be achieved when stopping the proliferation of the tumor cells only. More importantly, it is necessary that the tumor and all pathogenic cells whether present in the solid tumor or present as dissimilated cells, are removed e.g. by killing the tumor cells. Thus, full remission can be achieved. Typically, the removal of pathogenic cells may be obtained by surgery or by the induction of cell death. It is well known that the abnormal inhibition of apoptosis is a hallmark of cancer or other diseases. That is, it is desirable to treat tumor diseases not only by stopping the proliferation of tumor cells but also by inducing cell death of the tumor cells. A possibility to drive cell into the cell death is to induce the cell death program by apoptosis.
Thus, one object of the present invention is to provide a method for inducing or enhancing the apoptosis of tumor cells or precursor cells thereof of breast cancer and malignant melanoma.
In an another aspect, the present invention relates to a method for inducing or enhancing the apoptosis of tumor cells or precursor cells thereof of gynaecological cancers, like endometrial cancer or ovarian cancer. Furthermore, the present invention aims to provide a method for reducing the number of tumor cells and precursor cells thereof.
In addition, the present invention provides GnRH II antagonists being superior over the hitherto described GnRH II antagonists in view of their activity and their capacity of enhancing apoptosis in tumor cells.